1. Field of the Invention
The present invention relates generally to radio broadcasting and receiving systems, and more particularly to radio broadcasting and receiving systems wherein both frequency modulated audio and textual information are transmitted and demodulated at a receiver. The textual information is stored and processed by a computer.
2. Background Art
The radio signal transmitted from a FM station is an electromagnetic wave which frequency shifts according to the amplitude of the audio signals. The center frequency is the carrier frequency which is in the band of 88-108 Mhz for commercial FM stations in the USA. Each station has a bandwidth of 200 kHz and the audio frequency response is between 50 to 15000 Hz. According to the FCC regulations Part 73, Subpart B, subcarriers which carry other information are allowed to multiplexed with the main program. The subcarriers and their significant sidebands must be within the range of 20 to 99 Khz when monophonic program is broadcasting and 53 to 99 Khz for stereophonic program. This subcarrier multiplexing has been utilized for background music for restaurants and multilingual broadcasting. Subcarrier multiplexing has also been proposed for nationwide paging services, differential global positioning systems, and Radio Broadcasting Data Systems (RBDS or RDS) in which the station name and music format are transmitted as textual messages along with the main program.
References relating to the field of data communication are as follows:
U.S. Pat. No. 4,928,177 issued May 22, 1990 to Martinez entitled TWO-WAY DATA BROADCAST NETWORKS discloses a communication system wherein forward link communication is achieved utilizing a conventional television broadcast station, either utilizing an entire presently unused TV channel or in a shared TV mode, with the return link communication being achieved using narrow band communication techniques for relatively low data rate communication through conventional television receiver aerials to a central receiver near the television station transmitter. The carrier reference of a local AM radio station is used as a synchronizing reference for the data streams and to allow the very close separation of each band in the return communication link to allow a large number of remote receivers to simultaneously communicate in the reverse link. Alternatively, the TV Chroma subcarrier serves this purpose.
U.S. Pat. No. 4,512,025 issued Apr. 16, 1985 to Frankel et al. entitled INCREASING CAPACITY OF BASEBAND DIGITAL DATA COMMUNICATION NETWORKS discloses broadband network capabilities for baseband digital collision detection transceiver equipment for communication between a plurality of data stations by affording simultaneous transmission of multiple channels over a broadband pass transmission link such as coaxial cable. Thus, a fundamental carrier wave is transmitted on the link, received at local data stations and used to detect signals on different baseband channels for reception. For transmission the carrier wave typically is used for segregating a plurality of at least two transmission channels into typically single sideband upper and lower pass bands of baseband bandwidth capability adequately separated with guard bands to permit simple separation for receiving by means of pass band filters, etc.
U.S. Pat. No. 4,280,020 issued Jul. 21, 1981 to Schnurr entitled RADIO TELEPHONE SYSTEM WITH DIRECT DIGITAL CARRIER MODULATION FOR DATA TRANSMISSION discloses a radio-telephone system which transmits data and speech on separate sideband channels. The data and the speech signals are separated in the frequency domain, and are transmitted in respective separate sideband channels. The data sideband channel contains sidebands generated by time coding an otherwise continuous wave signal. The latter signal may be a carrier signal which is modulated to convey the speech signals.
U.S. Pat. No. 3,986,122 issued Oct. 12, 1076 to McManus entitled RELIABLE COMMUNICATIONS SYSTEM discloses a communication transmitter system having an upper and lower sideband containing a digital word which can be complemented to indicate information content having serial register means adapted to receive digital information for generating a digital word and having inputs and outputs; parallel register means operatively connected to the output of said serial register means for storing the output of said serial register; modulating means operatively connected to the output of said parallel register means for generating upper and a lower sidebands; each of said sidebands containing said digital word complementing means operatively connected to said modulating means for complementing one of said upper and lower sidebands; and radio frequency transmitter means operatively connected to the output of said complementing means and said modulating means for transmitting said upper sideband and lower sideband simultaneously.
U.S. Pat. No. 3,967,202 issued Jun. 29, 1976 to Batz entitled DATA TRANSMISSION SYSTEM INCLUDING AN RF TRANSPONDER FOR GENERATING A BROAD SPECTRUM OF INTELLIGENCE BEARING SIDEBANDS discloses a data transmission system which uses multiple sidebands for separate data transmission and includes an interrogate source for transmitting RF interrogate signals to the locations of the data sources and a transponder associated with each data source for receiving the interrogate signals and for generating FR reply signals representing the information. The transponder includes a transmitter having a voltage controlled oscillator responsive to data signals at first and second levels to generate sinusoidal output signals at first and second frequencies, respectively, a wave shaping circuit which converts the output signals to sawtooth wave signals at the corresponding frequencies and an FM oscillator for providing a carrier signal which is modulated by the sawtooth signals to produce a broad spectrum of sideband signals of approximately equal amplitude.